1. Field of the Invention
The present invention relates to a display unit comprising a flat display substrate which has pixels disposed at points of intersection between scanning lines and signal lines, and a peripheral driver circuit substrate mounted on the flat display substrate, and a method of manufacturing such a display unit.
2. Description of the Related Art
Conventional liquid crystal display units have driver IC chips which have typically been p-SiTFT driver IC chips each comprising polycrystalline silicon thin-film transistors (hereinafter referred to as "p-SiTFT") disposed on a surface of a glass substrate. Liquid crystal display units with such p-SiTFT driver IC chips are disclosed in Japanese Patent Laid-open patent publication No. 88971/94 and Japanese Patent Laid-open patent publication No. 333645/95.
As shown in FIG. 1 of the accompanying drawings, a conventional liquid crystal display unit with p-SiTFT driver IC chips has a display area 157 on a surface of a liquid crystal display substrate 101 which is a flat display substrate. The display area 157 comprises a plurality of gate bus lines 156 as horizontal scanning lines and a plurality of data bus lines 155 as vertical signal lines. Source driver IC glass chips 102 and gate driver IC glass chips 103 are directly mounted on another area of the surface of the liquid crystal display substrate 101 than the display area 157. These driver IC glass chips 102 are mounted on the liquid crystal display substrate 101 by the COG (Chip-On-Glass) technique. The source driver IC glass chips 102 are electrically connected to the data bus lines 155, and the gate driver IC glass chips 103 are electrically connected to the gate bus lines 156.
Each of the gate driver IC glass chips 103 comprises a peripheral driver circuit (not shown) for driving gate bus lines 156 and a peripheral driver circuit substrate (not shown) on which the peripheral driver circuit is mounted. There are four gate driver IC glass chips 103 arranged in a vertical array. Each of source driver IC glass chips 102 comprises a peripheral driver circuit (not shown) for driving data bus lines 155 and a peripheral driver circuit substrate (not shown) on which the peripheral driver circuit is mounted. There are ten source driver IC glass chips 102 arrayed in a horizontal row.
p-SiTFT driver IC chips are usually disposed in a closely spaced pattern on a surface of a glass substrate which is used as a liquid crystal display substrate. Therefore, the driver IC chips and the liquid crystal display substrate have equal or close coefficients of thermal expansion. Even with the driver IC glass chips mounted on the liquid crystal display substrate by the COG technique, junctions of electrodes of the driver IC glass chips are free from disconnections due to different thermal stresses in the driver IC glass chips and the liquid crystal display substrate. As a result, highly reliable liquid crystal display units can be manufactured with a high yield.
If single-silicon driver IC glass chips are mounted on a liquid crystal display substrate by the COG technique, then junctions of electrodes of the driver IC glass chips tend to be disconnected because of different coefficients of thermal expansion of the driver IC glass chips and the liquid crystal display substrate.
For mounting p-SiTFT driver IC chips on a liquid crystal display substrate, therefore, the COG technique has been used taking the advantage of the same coefficients of thermal expansion of the p-SiTFT driver IC glass chips and the liquid crystal display substrate.
As shown in FIG. 2 of the accompanying drawings, a conventional liquid crystal display unit has a liquid crystal display substrate 111 as a flat display substrate and an opposite substrate 123 which are joined to each other by a seal 124 interposed therebetween. A liquid crystal 125 is sealed between the liquid crystal display substrate 111 and the opposite substrate 123. The liquid crystal display unit also includes a plurality of scanning lines and a plurality of signal lines extending perpendicular across the scanning lines, the scanning lines and the signal lines being disposed on a surface of the liquid crystal display substrate 111 which faces the opposite substrate 123.
A driver IC glass chip 112 comprises a glass substrate 112a as a peripheral driver circuit substrate, a driver IC 114 as a peripheral driver circuit, a driver IC input electrode 113, and a driver IC output electrode 115. The driver IC 114, the driver IC input electrode 113, and the driver IC output electrode 115 are disposed on a surface of the glass substrate 112a. The driver IC input electrode 113 and the driver IC output electrode 115 are electrically connected to the driver IC 114.
An input electrode 122 of a scanning line or a signal line is disposed on a surface of the liquid crystal display substrate 111 which faces the liquid crystal 125, and extends from a display area where the liquid crystal 125 is sealed. An interconnection electrode 121 is also disposed on the surface of the liquid crystal display substrate 111 which faces the liquid crystal 125. The driver IC input electrode 113 of the driver IC glass chip 112 is electrically connected to a flexible printed circuit board 132 by the interconnection electrode 121.
For mounting the driver IC glass chip 112 on the liquid crystal display substrate 111 by the COG technique, a bump 116a is formed on the surface of the driver IC input electrode 113, and a bump 116b is formed on the surface of the driver IC output electrode 115. A surface of the driver IC glass chip 112 which faces the driver IC 114 is then mounted on the liquid crystal display substrate 111 by the face down bonding. The bump 116a is bonded to the interconnection electrode 121, electrically connecting the driver IC input electrode 113 to the interconnection electrode 121 through the bump 116a. The bump 116b is bonded to the input electrode 122, electrically connecting the driver IC output electrode 115 to the input electrode 122 through the bump 116b. Thereafter, a protective resin body 117 is formed around the junctions between the driver IC glass chip 112 on the liquid crystal display substrate 111 and also around the driver IC 114. In this manner, the driver IC glass chip 112 is secured in position and protected by the protective resin body 117.
The flexible printed circuit board 132 comprises an insulating film 120, a conductor 119, and an insulating film 120a. The conductor 119 is disposed on a surface of the insulating film 120, and the insulating film 120a is disposed on an area of a surface of the conductor 119 other than an area thereof reserved for electrical connection. The area of the conductor 119 reserved for electrical connection, i.e., an end of the conductor 119, is pressed and bonded to the interconnection electrode 121 through an anisotropic conductive film 118. The conductor 119 is thus electrically connected to the interconnection electrode 121 by the anisotropic conductive film 118.
The conductor 119 has an opposite end electrically connected to an output electrode of a driver circuit on a driver circuit board (not shown), which serves to supply a power supply voltage and transmits a control signal to the driver IC 114. Therefore, the output electrode of the driver circuit on the driver circuit board and the driver IC input electrode 113 are electrically connected to each other by the conductor 119, the anisotropic conductive film 118, the interconnection electrode 121, and the bump 116a.
In the conventional liquid crystal display unit shown in FIG. 2, the driver IC glass chip 112 is mounted on the liquid crystal display substrate 111 by the COG technique. According to the COG mounting process, the bumps 116a, 116b need to be formed respectively on the driver IC input electrode 113 and the driver IC output electrode 115 of the driver IC glass chip 112. The need to form these bumps 116a, 116b is responsible for limitations posed on efforts to lower the cost of the liquid crystal display unit.
A packaging technique known as TCP (Tape Carrier Package) which has widely been used for mounting single-crystal silicon driver IC chips on liquid crystal display substrates is applied in some instances to the mounting of TFT driver IC chips. The TCP technique also requires a bump forming process, a bonding process, and a resin sealing process. Accordingly, the TCP technique as applied to the mounting of TFT driver IC chips has prevented liquid crystal display units from being lowered in cost.